Unit type airplane heater



l I l I I v v I June 14, 1949. r F. o. HESS 'ETAL 2, 3,

' UNIT TYFE AIBfLANE HEATER Fild June 20, 19,44 v e Sheets-Sheet 1 INVENTORS W 0. "Q4 L f- "w BY KM L. 0M 3*- W ATTORNEY June 14, 1949. F. o. Hess ETAL uuiw rYrE AIRPLANE HEATER 6 shee'ts' sheet 2 Filed June 20. 1944 INVENTORS FWD.)

' WEN .KnAl -.D1d-l8- ATTORNEY June 14, 1949. v F. o. Hess ETAL I l 2,473,372

I UNIT TYPE AIRPLANE HEATER Fi1gdune 20, 194'4 ,s Shee'ts-Sheet 3 Is 7 a:

mm by w IINVENTORS FM 0. i

ATTORNEY .June 14, 1949. I F. o. HESS 'ETAL 2,473,372

um'r TYPE AIRPLANE HEATER Filed June 20, 1944 e Sheets-Sheet 4 III ' INVENTORS FM o Mel- BY mu. zmxw-9- i4 ATTORNEY June 1 4, 1949. F. o. HESS EI'AL 2,473,372

UNIT TYPE AIRPLANE HEATER Filed June 20, 1944 e Sheets-Sheet 5 INVENTORS iQ %oRNEY June 14, 1949. F. o. HESS ErAL ,UNIT TYPE AIRPLANE HEATER 6 Sheets-Sheet 6 Filed June 20, 1944 INVENTORS PM o. n Lam -Q F.

BY km L. 0W

MTTORNEY' Patented June 14, 1949 UNITED STATES PATENT OFFICE 2.473372 g UNIT TYPE AIRPLANE HEATER Pennsylvania Application June 20, 1944, Serial No. 541,258

7 Claims. 1

This invention relates to heaters, and is especially concerned with heaters of the kind operated with a gaseous or liquid fuel.

While the heater of the invention is of great utility for effecting heating wherever a compact heater of light weight is required in which the heat output per pound of heater is exceptionally high, it is especially useful for heating airplanes. The present tendency toward self-contained heaters which are compact and of unusually large heating capacity has brought about an intensive study of the problem of improving the performance and operation of heaters, This is especially true of aircraft heating in which the heater must be light in weight and as small as possible so that it will occupy a minimum amount of space. Further, a heater suitable for airplane heating must be capable of producing large quantities of heat to maintain the interior of an airplane comfortable when the temperature of the atmosphere may be as low as minus 60 F., and when the airplane is at ground level and in flight at altitudes as high as 40,000 feet and higher. Since the density of air at altitudes of 22,000 feet and 40,000 feet is about onehalf and one-fourth, respectively, of the density of air at sea level, it will be evident that provision must be mad to maintain the proper ratio of air to fuel as well as insure stable combustion conditions at all times, so that reliable heater operation will be effected under all of the operating conditions encountered in aircraft heating.

Itis an object of the invention to provide an improved self-contained heater which is extremely eflicient and compact and in which the heat output per pound of heater is exceptionally high.

Another object of the invention is to provide such a heater which is capable of maintaining the interior of an airplane comfortable and perform-s reliably under all of the operating conditions encountered in aircraft heating.

A further object of the invention is to provide an improved heater having a refractory lined combustion chamber in which the lining is heated to incandescence to promote substantially complete combustion of a fuel mixture and also accelerate the rate at which combustion is effected.

A still further object of the invention is to provide an improved heater having a heating space in which the pressure may be reduced .below that of atmospheric pres-sure without having the full effect of, such reduction in pressure reflected back to a combustion chamber in which combustion is accomplished and. from which high temperature heating gases pass into the heating space. e

A still further object of the invention is to provide an improved heater including an impeller housing, electric driving motor, burner and heat exchanger constructed as a single unit and in such a manner that the heater parts are accurately aligned and rigidly secured to the impeller housing.

A still further object of the invention is to provide an improved self-contained heater of simplified construction which can be readily assembled. 1

The novel features which we believe to be characteristic of our invention are set forth with particularity in the claims. The invention, both as to organization and method, together with further objects and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawings forming a part of this specification, and of which: 7

Fig. I is a vertical sectional view, taken on lines l-I of Figs. 2, 3 and 8, of a heater em bodying the invention;

Fig. 2 is a horizontal sectional view, taken on line 2-2 of Fig. 1, to illustrate parts of the heater more clearly;

Fig. 3 is a horizontal sectional view taken on line 33 of Fig. 1;

Fig. 4 is a side elevation of the heater illustrated in Figs. 1 to 3 removed from the casing;

Fig. 5 is a side elevation, partly broken away, /of the heater casing within which the unit shown in Fig. 4 is positioned;

Fig. 6 is a fragmentary vertical sectional view, taken on line 6-6 of Fig. 3, to illustrate the burner more clearly;

Fig. '7 is a fragmentary sectional view taken on line 1-1 of Fig. 2;

Fig. 8 is a fragmentary sectional view taken at line 8-8 of Fig. 1;

Fig. 9v is a view diagrammatically illustrating an electrical control system for the heater shown in Figs. 1 to 8 inclusive;

Fig. 10 is a vertical sectional view of a heater, similar to Fig. 1 and taken on line l0l0 of Fig. 12, illustrating a modifiation of the invention;

Fig. 11 is a horizontal sectional view of the heater shown in Fig. 10;

Fig. 12 is a fragmentary vertical sectional view taken at line I 2'l2 of Fig. 10;

Fig, 13 is an enlarged perspective view of a part of the heater shown in Figs. and 11, to illustrate a detail more clearly;

Fig. 14 is a cross sectional view of an airplane diagrammatically illustrating a heater therein like that of Figs. 1 to 9 or Figs. 10 to 13 inelusive; and

Fig. 15 is a fragmentary plan view looking down upon the heater shown in Fig. 14.

Referring to Fig. 1, a heater which is shown embodying the invention includes a pair of adjacent bodies or plates l0 and H providing a fan or impeller housing which forms an outer annular diffusing chamber l2 and an inner chamber l4 in communication therewith and within which is disposed a rotatable impeller 15. The impeller l5 includes a bottom circular disk 16 having integrally formed therewith a plurality of vertical fins or blades H in spaced apart relation and extending radially outwardly from the hub to the peripheral edge of the disk It. A suitable gasket I8 is interposed between the ribbed surface portions at the peripheral edges of the plates [0 and H which are secured together by anumber of screws H], as shown most clearly in Fig. 2.

A motor 20 is secured to the impeller housing by studs 2| which extend through tubes 22 formed integrally with plate In and against the bottom ends of which the motor is tightly drawn. A shaft 23 of the motor 20, to which the impeller 15 is secured by a set screw 24, extends upwardly into the chamber l4 through a hollow sleeve 25 which is also formed integrally with plate H]. The hub of the impeller l5 and upper end of sleeve 25 are formed to provide a labyrinth packing 26, and the sleeve may be provided with a packing gland 21 at its lower end for the shaft,

so that leakage from the chamber M will be prevented. The tubes 22 accurately align the impeller, parts and the motor shaft 23 and, together with the studs 2|, provide a rigid and unitary impeller and motor construction.

A casing 28 provided with a flange 29 at its lower open end is secured by screws 30 to a boss or raised portion at the top face of plate II, as shown most clearly in Fig. 2. The flange 29 is of irregular shape and the boss on the plate II to which it is secured is of similar shape, so that the casing 28 can be secured to the plate I I only when the flange 29 and boss are in alignment. The casing 28 is open-ended to receive an insert having a closed cylindrical head 3i at one end and a hollow tubular part 32 at the opposite end which are connected by an arcuateshaped wall section 33, as shown in Figs. 1, 2 and 7. As seen in Fig. 7, one end of the wall section 33 adjacent the tubular part 32 is formed with a shoulder 34 which fits against one end wall of the casing 28, and the closed cylindrical head 3| is provided with a flange 35 which is secured by screws 36 to bosses formed at the end wall of casing 28.

A butterfly valve 31 having an opening 38 therein is pivoted at 39 within the tubular part 32 and pivotally connected by a link 40 to a pin M which is secured to one end of a bellows 42. A threaded pin 43 secured to the opposite end of bellows 42 passes through a slightly enlarged unthreaded opening in the cylindrical head 3| and receives a lock nut 44. The initial adjustment of the bellows 42 is accomplished by moving the lock nut 44 on the pin 43, and the lock nut 44 is held firmly against the cylindrical head 3| by a coil spring 45 disposed about the pin 43 between the bellows 42 and the inner surface of the cylindrical head. The bellows 42 operates responsive to atmospheric pressure to move the butterfly valve 37 from its closed position with decrease in atmospheric pressure and toward its closed position with. increase in atmospheric pressure to control the flow of air into the tubular part 32 during operation of the heater, as will be explained hereinafter.

In order to insure proper alignment of the bellows 42 and link 40 and always obtain accurate movement of the butterfly valve 3! with expansion and contraction of the bellows, the pin 41 engages and freely moves past the tapered end of a guide plate 46 which is formed integrally with and is at right angles to the wall section 3|.

An .electrical heating element 41 is mounted on the plate ll directly over the central opening 48 therein which constitutes the air inlet to the chamber I4. The heating element 41 comprises three superimposed flat plates 49, 50 and 5| each having an opening approximately the size'of the opening 48 in plate II, as shown in Fig. 1. A wire 52 is wound or coiled about the intermediate plate 50 with adjacent turns close togetherv and distributed over the entire area of the opening in the plate, as best shown in Fig. 2. The three fiat plates are secured together in any suitable manner, and the bottom plate 5i may be'provided with lugs 53 at each end, one of which is seen in Fig. 1, at which regions the heating element may be secured by screws (not shown) to the plate H at each side of the opening 48. The flat plates 49, 50 and 5| may be formed of any suitable insulating material and the wire 52 may be of a suitable high resistance'alloy, such as, for example, nichrcme and the like. As shown in Fig. 1, the heating element 41 may be provided with suitable terminals 54 to which the ends of the wire 52 may be secured, as by brazing, for example.

Intermediate the ends of casing 28 and at one side thereof is integrally formed a hollow vertical post 55, as best shown in Figs. 1 and 2. The passage or opening 56in the bottom part of post 55 is of reduced diameter, and at its lower end is threadedly secured an orfice member 51. The opening 56 is in alignment with an opening 58 in plate II which in turn is in communication with chamber 14 at a region between the hub and peripheral edge of the impellerl5. The passage or opening of larger diameter in the upper part of post 55 receives a suitable filter 59 having a flange 60 at its lower end. The filter 59 is held in position by a tubular member 6| which fits against the flange 60 in the space between the filter and inner surface of the post 55, and is threadedly secured at an intermediate region to the upper end of the post 55. The upper end of tubular member fil is provided with a nipple connection 62 to connect the tubular part to a suitable source of supply of liquid fuel, such as, forexample, gasoline and the like.

Air for combustion is drawn through the inlet or tubular part 32 past the butterfly valve 31 and flows downwardly within casing 28 into the inner chamber M of the impeller housing. This movement of combustion air is effected by the impeller l5 into the path of movement of which is discharged liquid fuel issuing from the orifice member 51. Atomization of the liquid fuel is effected by the impeller l 5, and the mixture of combustion air'and atomized fuel passes radially outward into the annular or circular diffusing chamber l2.

As shownmost clearly in Figs. 4 and 8, the bottom plate II] is provided with a short hollow leg 65 having a passage 66 therein which is in communication with the diffusing chamber l2. The upper part of passage 66 is formed with a ramp 6! which slopes downwardly in the direction of rotation of the impeller 15. The bottom plate It is also formed with a lug or block 68 having one face thereof in vertical alignment with the straight sid wall of passage 66, as seen in Fig. 8. The block 68 fits snugly between the plates l and II when the latter are secured together and is slightly narrower than the width of the diffusing chamber I2 to provide a gap 69 at the inner wall of the diffusing chamber, as shown most clearly in Fig. 1. By providing the block 68 and hollow leg 65 with the ramp 61, a right angle change in the direction of flow of the air and fuel mixture is readily effected from the horizontally disposed diffusing chamber l2 into the vertical passage 66.

Th hollow leg 65 is provided with a flange 18 at its lower end, and to this flange is removably secured at H, as by screws, for example, the upper open end of a vertical metal shell 12. The shell 12 is normal to the plane of rotation of the impeller l and forms a housing for a burner including a manifold 13 having an upper inlet end M of reduced cross section which fits snugly within the lower end of passage 6', as shown in Figs. 6 and 8. A side wall 15 of the manifold 13 is formed with a plurality of small apertures or openings 16 which are disposed in vertical rows extending the full length of the inlet'chamber H formed by the manifold 13. The side wall #5 is provided with a plurality of ridges 18 extending the full length of the manifold 13 to form small channels or grooves '59 into which the mixture of air and fuel is discharged from the outlet ends of the small openings 16.

The apertured wall 15 forms the inlet of a refractory lined combustion chamber 80 having two spaced apart elongated outlets 8f substantially coextensive with the manifold f3. As shown in Figs. 1, 3 and 6, a hollow rectangular block 32 formed of a suitable high temperature refractory material, such as, for example, silicon carbide and the like, is positioned within the metal shell 12 to provide the refractory lining for the combustion chamber 8|]. The refractory block 82 bears against the side walls of the metal shell l2 and at one end overlies the peripheral edges of the apertured side wall 15. The opposite end of the refractory block 82 adjacent the outlets 8| fits snugly against an end wall of the metal shell 12, as seen in Figs. 3 and 6.

The top and bottom of the refractory block 82 are notched at their inner surfaces at 85 to receive the upper and lower ends, respectively, of a vertical post 84 which is also formed of a suitable high temperature refractory material, such as, for example, silicon carbide and the like. The post 84 is of the shape shown in Fig. 3. and,

when the post is held in the refractory block 82 and the latter is positioned within the metallic shell 12, the widest flat side of the post bears against an end wall of the metal shell 12 within which are housed the burner parts just described.

The metal shell 1?. is formed with several threaded openings which are in alignmentwith openings in the hollow refractory block 82 when the latter is disposed within the metal shell, as shown in Fig. 1. An electrical ignitor 85 is threadedly secured to one of the openings inthe shell 12 to effect combustion of the mixture of air and fuel supplied to the combustion chamber 80. The electrical ignitor may be of a hot wire type having a heating element 86, and the inner part 81 extending through the opening in the refractory block 82 may be formed of a suitable high temperature refractory material which will withstand the high temperatures produced within the combustion chamber 80. A hollow tube 88 having a suitable glass partition therein is threadedly secured to the other opening in the metal shell 72 and serves as an observation port through which the combustion chamber may be viewed.

The heated products of combustion produced in combustion chamber 80 pass through the outlets 8! into a pair of hollow heat dissipating elements 89 which are annular in form and one of which is concentric within the other. Each element 89 is formed of spaced apart sheets of metal 9e and 9f united at their top and bottom edges by welding. The vertical edges of the metal sheetsat one end of the elements 8% are welded to the metal shell 12 at the regions of the combustion chamber outlets 8 I, and the vertical edges thereof at the rear of the metal shell 12 are united by welding, as shown most clearly in Fig. 3. The heat dissipating elements 39 form annular heating spaces 92 of substantially the same height as the combustion chamber 80 and provide paths of flow for the heated products of combustion which are considerably longer than the heights of the heating spaces. The products of combustion pass from the elements 89 through an outlet 93 which is connected by a tube 93a to both of the heating spaces 92. As shown in Fig. 3, the ends of the elements 89 adjacent the outlet 93 are connected to each other at as and to the metal shell f2 by a bracket 95, so that accurate positioning of the elements 89 with respect to other parts of the heater will be obtained.

An outer casing 95 having a plurality of rectangular duct sockets 91 at its upper part err-- closes the elements 89. The bottom plate Ill of the impeller housing is provided with a number of spaced apart pins 98 at its periphery which fit into bayonet slots 98 at the top edge of casing 96 for removably securing the latter to the impeller housing, as shown most clearly in Figs. 4 and 5. As shown in Fig. 3, a number of U-shaped straps lllfi are welded to the inner surface of casing 96 and bear against the lower part of the outer element 39 to hold the elements in position and form an annular space it! of substantially uniform width between the outer element 89 and casing 96.

Between the motor 2% and inner element 59 is positioned a shield H32 of sheet metal which is annular in form and flares outwardly at its upper end. The shield m2 is secured by screws its to the underside of plate 10 and is formed with slots HM at the regions of the duct sockets as shown most clearly in Fig. 1. The annular spaces HM, I05 and H36 serve as paths of flow for air to which heat is given up by the heat dissipating elements 89. The air to be heated is circulated through the heater by a fan fill which is fixed to a shaft m8 extending down wardly from the motor 2B. The fan it! is positioned in a space Hi9 between the elements and an end cover I It which is removably secured at l l I to the casing 96 and provided with a screen H2 through which is drawn air to be heated. The air circulating fan If)? is of a propeller type which is designed as a volume fan in contrast to acrea e 7 a pressure fan and capable :of circulating lamge volumes .of air.

Liquid fuel is supplied :under pressure to the :heater just described by :a pump IM which is .driven by anelectricrnotor .I FI 5,.as-shown in Fig. '9. The pump H4 is connected by a conduit I'IB to a suitable source of supply of liquid fuel :and delivers fuel under pressure throughxa conduit =.I H which is connected to the nipple connection 62 at the top of :post '55. The motors :20 and H5 are connected by conductors H 8 and H9 and a double pole switch I29 to the positive side I 21 of :a suitable .direct current source of electrical energy having its negative side I22 grounded at 1:23,. The circuits for the motors 20 and 115 are completedby ground connections indicated at I24 and I25, respectively.

In the conduit I I'I is provided'a solenoid opera-ted control device which includes a valve 125 operated by a solenoid coil I2'I -having one terminal grounded at I28 and the opposite terminal connected by a conductor I29 to the conductor M9. The ignitor 85 is connected in a conductor I30 which connects motor 20 to ground at 121, and the air heater 4'! is connected in a conductor I31 having one end' connected to conductor 1 I8 and its other end grounded'at I32.

Three thermal devices I33, I 34 and I35 are provided in the electrical circuits just described to control the operation of the heater. The thermal device I33 is provided in a conductor $36 which is connected at one end to conductor I30 between the motor I20 and ignitor 85, and grounded at its other end at I37. The thermal device I34 is provided in conductor I3I between conductor I I8 and the air'heater 41, and the thermal device I35 is provided in conductor I29 "between solenoid coil I 2! and conductor H9. Although the thermal devices 133, I34 and I35 are diagrammatically illustrated as being of a bimetallic type, it is to be understood that the thermal devices may be of any suitable type and positioned within the duct sockets 91, as diagrammatically shown in Fig. 1.

When it is desired to operate the 'heater the switch 120 is closed to complete the electrical circuits for the motors 28 and I i5. When operation of the heater 'is first started the thermal device I35 is closed, so that closing of switch I20 also completes the circuit for solenoid coil I2I to cause opening of valve I26. With motor II 5 energized and driving pump II4, liquid fuel received from the source of supply through conduit H6 is pumped through conduit II.'I past valve 126 into the upper part of hollow post 55 to which the conduit III is connected, as previously described. The liquid fuel passes through the filter 59 which holds back any foreign matter which may accompany the fuel, and the fuel then flows downwardly through passage 56 and is discharged from the orifice member 5! into the impeller chamber I 4 through the passage 58 in the plate II.

The motor 2.0, which is energized when the switch I29 is closed, drives the impeller I5 to cause air for combustion to be drawn into the inlet or tubular part 32. The combustion air is drawn past the butterfly valve 31 and flows downwardly in casing 28 through the air inlet opening 68 into the chamber Id of the impeller housing formed by plates I and II. The small stream of liquid fuel squirting downwardly into chamber I4 from the orifice member 51 strikes the rotating impeller I and is mechanically atomized and mixes with the combustion air. The mixture of combustion air and fuel, which isiin :liquidphase .blitlifl'ilIfiSt-DI spray form, passes from chamber -11 to'theaannular diffusing chamber 1-2 in which-uniform mixing of the fuel and combustion air takes place. The impeller I5 is driven in a clockwise direction as viewed in'the drawings, and in the direction indicated by the arrow 138 3 and 8. Thus, the air and :iuel mixture passes from the horizontal annular chamber I2 into vertical pasage '66 in the direction indicated by the-arrows in Fig. 8, the downawardly sloping ramp BI the upper part of passage'fifi and block 58min the annular passage I2 providing an efficient arrangement to cause a change in direction of the air and fuel mixture from the annular chamber I2 into the vertical manifold I13. The gap 69 at the inner surface of the block '68 permits some of the air and fuel mixture to recirculate about the annular chamber as and prevents the ?build-ing up of an excessive pressure in the part of the annular chamber communicating with the vertical passage 66. The part of the annular chamber :I2 into which some of the :air and fuel mixture passes through the gap '69 is a regional reduced pressure in which eddiesa-re produced, thereby contributing to the uniform mixing of the-combustion air and atomized fuel in the annular chamber before the mixture passes :into the manifold I3 through the vertical passage 66.

The mixture of air and fuel passes from the manifold I3 through the small inlet openings I6 into the refractory lined combustion chamber 89 in which ignition of the combustible mixture is .efiected by the .ign'itor 8-5. As seen in Fig. 9, the ignitor :85 *isconnected in series relation with the motor 20 and is energized when the switch 12!] is closed to start operation of the heater. By providing -'a large number of small inlet openings 15 through which the mixture of air-and fuel is discharged fr'om manifold I3, as best seen in Fig. 1, the mixture is subdivided into a multiplicity of small streams which project into the combustion chamber '80. When ignition is effected a plurality of small flamesare produced, and the flames thus produced and maintained at the apertured inlet '15 are distributed over an area substantially coextensive with the cross sectional area of the combustion chamber .89.

By providing a large number of small inlet openings I6 to produce a multiplicity of relatively small and short flames, a substantial portion of the burning of combustion is initiated at the region of the refractory lined combustion chamber adjacent to the inlet. With this arrangement a relatively high average temperature is produced and developed at the inlet end of the combustion chamber 80. After a short interval of time, the flames maintained in the combustion chamber effect such heating of the refractory lining that thelatter is heated to a high incandescent temperature.

The heating of the refractory lining to incandescen'ce contributes to the maintenance of high combustion chambertemperatures and also brings about rapid flame propagation. This is clearly evident by the change in length of the flames as the refractory lining becomes heated. Each of the flames produced at the apertured inlet wall "consists of an inner cone of unburned air and fuel and an outer cone constituting the portion of the flame in which the combustion reaction is taking place. When operation of the heater is first started and the refractory lining is relatively cool, the inner cones of the individual flames are relatively long in length. As the inner refracindividual flames become increasingly shorter and shorter; and, when the inner refractory lining becomes heated to incandescence, the inner cones of the individual flames become appreciably shorter from their original lengths when initially produced. This is due to the fact that the air and fuel mixture introduced into the combustion chamber in finely divided streams is subjected to intense heat radiated from the highly heated surfaces of the inner refractory lining, thereby effecting substantially complete burning of the mixture within the combustion chamber before the mixture reaches the outlets 8|.

When a mixture of air and atomized gasoline is supplied to the combustion chamber 80, combustion chamber temperatures as high as 2000 F. and higher are developed and maintained, and gases consisting substantially entirely of heated products of combustion are discharged through the outlets 8I into the heating spaces 92 of element 89 at a temperature nearly equal to the temperature developed in the combustion chamber. Since the mixture of air and fuel is introduced into the combustion chamber 80 at temperatures of 70 F. and lower, and are heated to a temperature of 2000 F. and higher, the gases expand at least four and one-half fold and at a rate directly proportional to increase in absolute temperature. In view of the fact that the gases undergo considerable expansion in the combustion chamber, relatively large volumes of high temperature gases are discharged from the combustion chamber into the annular heating spaces 92.

The channels or grooves 19 formed by the ridges I8 at the outlet ends of the small inlet openings I6 also contribute to the maintenance of the stable combustion conditions in the combustion chamber under widely varying operating conditions, as will be explained more fully hereinafter. When the mixture of air and atomized fuel is discharged from the openings 15 into the chamber I9, expansion of the mixture takes place in the channels with a corresponding decrease in the velocity at which the mixture enters the combustion chamber. In this way any tendency for the flames to blow off from the inlet openings 15 under adverse operating conditions is reduced, and the flames will always remain rooted to the discharge ends of the inlet openings.

The refractory post 84 forms a part of the refractory lining for the combustion chamber 80 and the surfaces thereof facing the interior of the chamber and the outlets 8| are also heated to incandescence to assist in bringing about substantially complete combustion of the air and fuel mixture in the chamber. In addition, the refractory post 84 heated to incandescence during operation of the heater serves to effect reignition of the air and fuel mixture in the event flow of the mixture is interrupted momentarily or operation of the heater is stopped for a short interval of time and is then resumed. The refractory post 84 also protects a portion of the shell I2 against which it bears from the high temperatures developed in combustion chamber 80. The refractory post 84 is shaped to subdivide the heated products of .combustion discharge from combustion chamber 80, so that the high temperature gases are divided more or less equally between the two heat dissipating elements 89;

Since the-air circulating fan I01 is driven by the motor 20, air is circulated upwardly through the heater when operation is first started by closing the switch I20. The air is drawn by the fan I01 through the screen IIZ into the space I09 and is then subdivided and passes upwardly through the annular spaces IOI, I05 and I06. Heat from the high temperature gases passing through the annular heating spaces 92 is given up to the air flowing upwardly in the spaces IOI, 505 and IE5, and the heated air is discharged from the heater from the duct sockets 91. The metal sheets 90 and HI forming the heating spaces 02 provide a relatively extensive heat transfer surface so that eflicient heating of air is effected. Since the chemical reaction of combustion is substantially completed in combustion chamber 80, and the high temperature gases enter the heating spaces 92 at practically the temperature developed in the combustion chamber, the maximum temperature differential between the high temperature gases and air to be heated is obtained at the region of the elements 80 adjacent the inlet end of the heating spaces 92. Since the high temperature gases flow horizontally about the annular spaces 92 and throughout the height of these, spaces, and the air to be heated flows vertically upwardly through the I annular spaces Iill, I05 and I06, the air is progressively heated as it passes upwardly over the outer surfaces of the metal sheets 90 and 9I and is heated to the highest possible temperature when passing over the extreme upper edges of the elements 80. Stated another way, there is a rising temperature gradient of the air passing upwardly through the annular heating spaces IOI, I05 and I06 and, since the coolest aircontacts the extreme lower edges of the elements 89, these regions of the elements are at the lowest temperature due to heat transfer from the high temperature gases to the air first contacting such regions. Since the extreme upper edges of the elements 89 are last contacted by the air to be heated, and these regions of the elements are at the highest temperature due to horizontal fiow of the high temperature gases in the annular spaces 92, the air passing upwardly through the annular spaces MI, 805 and I05 will be heated to the highest possible temperature at the instant the air passes out of heat exchange relation with the elements 89.

The air circulating fan IEB'I rotates in a clockwise direction as viewed in the drawings, and in the direction of the arrow I38 in Fig. 3. With such rotation of the fan I07, a whirling movement is imparted to the air passing upwardly in the annular spaces IilI, I05 and I06 which is in a clockwise direction and generally counter-current to the counterclockwise flow of the high temperature gases in the annular heating spaces 92 from the combustion. chamber to the outlet connection 93. By providing a heat exchanger in which the high temperature gases and air to be heated are in counterilow with the air leaving and last contacting the highest temperature regions of the elements 85, an efficient arrangement is provided for heating large volumes of air circulated through the heater by the fan I01.

The circulation of the fan I 01 in a clockwise direction also prevents excessive heating of the metal sheets 90 and SI at regions adjacent to the metal shell I2 in that portions of the air stream in the annular space I05 are constantly being positively directed against the closed end of the space I05 at the region of the vertical post 84, as best shown in Fig. 3. If the fan I0! circulated in a counter-clockwise direction, the part-ofthe space I05 adjacent the end closed 11 I all by the metal shellv 12 would form a region of lower pressure in whichrthe' movement of air is not as rapid as in other parts of the space in which positive flow of air takes place. In such lower pressure region localized eddying of air would occur with consequent excessive heating of the metal sheets 90 and 9|, because heat then would not be given up sufiiciently rapidly to the air to be heated from the parts of the metal sheets at the vicinity of the lower pressure'region.

Some of the air drawninto'the space I09 by the fan I01 also passes upwardly in the annular space between the motor 20 and shield I02 to effect cooling of the motor. After flowing over the surfaces of motor 20, such air passes through the slots I04 in shield I02 which'are directly opposite the duct sockets 91 and mixes with heated air passing upwardly through the annular spaces !I, I05 and I06. The upper flared portion of shield I02 providesa curved surface opposite the duct sockets 91, so that an abrupt change in direction of flow of heated air is avoided.

The annular heating spaces *92 provide a relatively long path of flow for the high temperature gases which is considerably longer than in prior heater constructions in whichthe high temperature gases simply pass in a path of flow substantially equal to the width of the metal sheets 90 and 0|. The spent products of combustion are discharged fromthe heating spaces 92 through the outlet connection 03 which is located in the extreme bottom part of the elements 39 at the rear of the metal shell '12, as best shown in Fig. 4.

After ignition has been accomplished in combustion chamber 80 and the heated air discharged through the duct sockets 91 is at a predetermined temperature, such as 160 F., for example, the normally open thermaldevice I33 in one of the duct sockets91 closes to complete a circuit from one terminal of mot0r-20 through conductors I30 and I36 to the ground connection at I31. In this way a low resistance circuit is completed for motor 20 around igniter 85-after ignition has been "established in combustion chamber 80, so that only asma'll current will pass through ignitor 85 during operation or the heater and thus prevent overheating or the heating element 86 which is constantly subjected to the high temperatures developed in the combustion chamber. 7

The thermal device I34 is normally open during operation of the heater and closes and completes the circuit for the air heater 41 when operation of the heater is first started by cl0sing the switch I20 and the temperature is below 70 F., for example. The air heater 41 is espeoially useful in certain applications of the heater, as will be described presently, and, when the need arises for heating-combustion air drawn into the inlet or tubular part 32-and prior to entering the impeller chamberI4, the air heater comes into play to heat the combustion air sufficiently so that reliable ignition of the mixture of air and atomized fuel will be obtained in the combustion chamber '80 under extremely cold operating conditions. After combustion is initiated in combustion chamber '80 and the air discharged from the duct sockets 01 is heated to about 10 F., the thermal device I3 located within one of the duct sockets opens to disconnect the air heater 41 from the source bi electrical supply.

The thermal device 135, which also located 1 within one of-theduct sockets 91, is normally closed and opens'when undesirable overheating of the heater occurs. When overheating. of the heater does occur, and the air is heated to a. predetermined high temperature of about 450 to 500 F., for example, the thermal device I35 opens and the circuit for the solenoid coil I21 is opened whereby valve I26 closes and shuts off flow of fuel to the heater. However, opening of the thermal device-I35 does not affect the energization of the motors 20 and I I5 and these motors will continue to drive the circulating fan I01 and fuel pump 4, respectively. The continued operation'offan I01 when overheating occurs tends to bring about rapid cooling of the heater; and, when the temperature of the heater falls below the predetermined high temperature, the thermal device I35 again closes to energize solenoid coil I21 and open valve I26'to permit fuel to be pumped to the heater. Thus, when overheating of the heater does occur the heater does not shut down completely but intermittent operation takes place whichis extremely desirable in certain uses of the heater. If the operating condition causing overheating of the heater persists, the heater will operate intermittently to effect heating of air until overheating occurs at which times combustion of air and fuel in combustion chamber is temporarily stopped. When the air temperature falls sufficiently to effect closing of thermal device I35, heater operation is again resumed in the manner just explained.

Although not to be limited theretogthe heater of the invention is especially adapted for use as an airplane heater. It is for this reason that the valve 31, the bellows 42 and interconnecting mechanism are provided to control the admission of combustion air tothe heater with changes in altitude ofan airplane in which the heater may be installed. The valve 31' and bellows 42- form what is referred to as an altitude compensator, so that larger volumes of combustion air may be supplied at increasingly higher altitudes to maintain a proper weight ratio of air to fuel as the air density decreases.

In the illustrated embodiment the valve 31 may be so adjusted that it is in its closed position when the heater is being operated'at sea level. In order to'provide an adequate supply of combustion air under these conditions, an opening 38 is formed in the valve 31, as shown most clearly in Fig. 7. It has been found that by making the opening 38 'of sufi'icient size, and driving 'the combustion air impeller with a series type motor'which increases in speed with increase in altitude, the altitude compensator-may be adjusted so that valve'31will remain closed to a predetermined high altitude of 15,000 'feet, for example, and yet provide s'ufiicient combustion air for maintaining stable combustion conditions in-combustion chamber 80.

At altitudes above the predetermined high altitude, however, the decrease in air density is such that it-is desirable to supply larger volumes o'f-air to the heater to maintain a desired weight ratio of airto fuel. Therefore, the bellows 42 and valve 31 are so adjusted that decrease in atmospheric pressure at altitudes above 15,000 feet, for

example, causes bellows 42 to expand and move valve- 31 from its closed position until it is fully open at an altitude of about 30,000 feet. This need for increasing the volume of combustion air supplied to the heater with decrease in air densi- "ty is necessary-because the rate at which fuel is supplied to the heater 'by' the pump I I4 is practlcally constant throughout all operating condition's Varying from sea level to an altitude of.30,000

feet or higher.

In Figs. to 13 inclusive is illustrated a modification of the invention which is generally like the heater shown in Figs. 1 to 8 and just described and differs therefrom primarily in that the altitude compensator and combustion chamber are of different construction. In order to simplify the description of the heater shown in Figs. 10 to' 13 inclusive, parts similar to those in the embodiment first described are referred to by the same reference numerals.

In Fig. 10 the altitude compensator includes a casing 28a provided at the lower open end with outwardly extending lugs (not shown) having openings to receive studs for removably securing the casing to the upper plate ll of the impeller housing in a manner similar to that shown in Fig. 2. A threaded pin 43a secured to the upper end of an expansible and contractible bellows 42a extends through a threaded opening in the upper part of casing 280. and receives a lock nut 44a. A vertically movable main valve 31a snugly fitting within the casin 28a is secured to the lower end of bellows 42a. The main valve 31a is formed with a cylindrical sleeve having a plurality of spaced apart U-shaped slots 3??) which terminate a short distance from the closed bottom of the valve. The bellows 42a operates responsive to atmospheric pressure to move main valve 31a downwardly with decrease in atmospheric pressure and upwardly with increase in atmospheric pressure.

Alongside of the chamber housing the bellows 42a is formed a vertical cylindrical space 38a having an inlet opening 38b. An auxiliary valve 38c within space 38a is secured to a stud 38d which threadedly engages an opening in casing 28a. The

position of the auxiliary valve 380 with respect to the opening 38b is adjusted by axial movement of the stud which may be held in any desired position by a lock nut 38e.

The main valve 31a is preferably adjusted so that it is in a closed position when the heater is being operated at sea level. Under these conditions combustion air is supplied through inlet opening 381) and passage 38a into the inlet 48 of the impeller chamber 14. As in the embodiment first described, the altitude compensator may be adjusted so that main valve 31a will remain closed to a predetermined high altitude and auxiliary valve 380 positioned to provide suflicient combustion air under these conditions to maintain stable combustion in the heater.

At altitudes above the predetermined altitude, such as 15,000 feet, for example, the decrease in air density makes it desirable to supply larger volumes of combustion air to maintain the desired weight ratio of air to fuel. Hence, the bellows 42a and valve 31a are so adjusted that decreases in atmospheric pressure at altitudes above 15,000 feet, for example, causes bellows 42a to expand and partially open the slots 31b, whereby additional combustion air is drawn in through the slots 28b at the top of casing 28a, the interior of easing 28a and the slots 31b into the inlet 48 of the impeller chamber I4. The opening of the slots 31b in main valve 31a gradually increases with increase in altitude until the slots are wide open at a predetermined high altitude, such as 30,000 feet, for example.

The casing 28a is formed with a hollow post 55a similar to the post 55 in Fig. 1. Liquid fuel delivered from a source of supply in a manner similar to that illustrated in Fig. 9 and described above ispumped through a conduit which is connected to the. upper part'of post 55a. A filter element 59a is removably held in position within post 55 by a sleeve Bla threadedly secured to the post, and an orifice member 51a is threadedly fixed in position below the filter element. After passing through the filter element 51a, the fuel is discharged through orifice member 51a into the impeller chamber [4 in which the fuel is mechanically atomized by the impeller I5, and the mixture of combustion air and atomized fuel passes radially outward into the annular diffusing chamber I2.

As shown in Fig. 12, the bottom plate Ill of the impeller housing is formed with a hollow leg 65a secured at 55b to a hollow fitting 650 which in turn is removably secured at Ha to the upper open end of a metallic shell 12a in which the burner parts are housed. The hollow leg 65a and fitting 65c together form a vertically extending passage 66a which slopes and is inclined in the direction of rotation of the impeller [5, as in the embodiment first described. A block 68 having a narrow gap 59 at the inner face thereof is formed integrally with the bottom plate 10 at the region of the annular chamber I2 and in the vicinity of the passage 66a, as shown in Fig. 12, to effect an efficient change in direction of flow of the air and fuel mixture from the annular chamber l2 into the vertical passage 66a.

The burner housed in metallic shell 12a includes a sheet metal manifold 13 having an upper inlet end 14a which fits snugly within the bottom of the fitting 650. The side wall 15 of manifold 13 is formed with a plurality of small openings 16 and vertically extending ridges 18, as in the embodiment first described. In Figs. 10 and 11 the wall 15 is shown as being formed of a plurality of thin plates 15a of refractory material which are stacked together and held in place in the manifold 13 in any suitable manner. The individual plates 15a are formed with shallow grooves or channels which form the small openings 16 when the plates are stacked together.

The refractory lined combustion chamber 80a is formed by a hollow rectangular block 82 of suitable high temperature refractory material which fits snugly about the apertured wall 15, as best shown in Fig. 11. The metallic shell 12a, in the direction of flow of the fuel into chamber 80a, is longer than the shell 12 previously described and includes side walls 12b at an angle to the part of the shell within which is disposed the hollow rectangular block 82. The outer ends of the side walls 12b are secured, as by welding, for example, to the ends of the metal sheets 90 and 9| forming the annular heating elements 89. Within the part of the metal shell 1212 having the side walls 72b is disposed a block 84a of suitable high temperature refractory material, such as, for example, silicon carbide and the like. The block in horizontal cross section is of substantially the same shape and size as the trapezoidal space bounded by the side walls 121), outer end of block 82 and the extreme outer ends of the side walls 12b, as shown in Fig. 11, the side walls of the block 84a.converging slightly from the chamber a to the heating spaces 92 in the same manner as the side walls 12b.

The block 84a is formed with horizontal U- shaped slots at opposite sides of an upright portion 84b, the two vertical rows of slots forming passages 84c communicating at one end at 84c with the chamber 800. and at the other end at 849 with the heating spaces 92. The passages 840 are wider at the inlet ends 84e than-at the amaa'ra outlet ends ag and collectively form a restricted: outlet or discharge orifice through which high temperature gases pass from the combustion chamber 80a to the heating spaces 92. The block 84a when viewed from the combustion chamber 88a in the direction of the heating spaces 92 appears as illustrated in Fig. 13, the. face My: overlying and abutting the outer edge of the hollow rectangular block 82 at 84c and the face 84s. hearing against the wall 841:, at the inlet end of the heating spaces 92.

The face 84p of the refractory block 8411 forms a part of the refractory lining for the combustion chamber 800; and is heated to incandescence during operation of the heater to promote substantially complete combustion of the air and fuel mixture in the chamber, as in the embodiment first described. The face 84p when heated to incandescence also functions in the same manner as the refractory post B lin Fig. 3 to effect reignition of the air and fuel mixture in the event flow of the fuel. mixture is interrupted momentarily or operation of the heater is stopped for a short interval of time and is then resumed.

Substantially complete combustion of the air and fuel mixture is accomplished in combustion chamber 80a in the same manner explained above in connection with the first embodiment. By providing the restricted outlet at 84c, a pressure is developed in combustion chamber 80a which is higher than the pressure in the heating spaces 92 into which the high temperature gases pass through the passages Me. By heating the refractory lining to incandescence and developing as high a pressure as possible in combustion chamber Bfla, the temperature at which combustion is accomplished is increased so that rapid flame propagation and a high rate of combustion are effected.

In the embodiment of Figs. 10 to 13 the side walls 122) of the metal shell 12a form a continuation of the innermost and outermost metal sheets 90 and 9| of the heat dissipating elements 89, and heat is given up from the heated gases flowing in passages 840 to air to be heated which flows over the outer surfaces of the metal walls 121). The passages 84c gradually decrease in size from the inlet end 34a to the outlet end My in order that the heated gases will enter the heating spaces 92 at as high a velocity as possible after initial cooling of the gases in the passages 840, as the result of giving up heat to the air flowing over the outer surfaces of the walls 12b.

The high temperature gases pass through the annular heating spaces 92 and give up heat to air passing over the outer surfaces of metal sheets and BI in the same manner described above in the first embodiment. A plurality of vertical fins I40 are secured, as by welding, for example, to the metal sheets 90 and 9| to increase the effective heat dissipating surface of the elements 89.

As shown most clearly in Fig. I1, the discharge end of each heating space 92 is provided with a vertically extending bafile I4I which extends from the extreme bottom of the metal sheets 9i and terminates a short distance from the upper ends of the sheets. The bailies do not extend completely across the space between the sheets 90 and 9| but do serve to deflect the flow of a substantial portion of the gases upwardly over the top edges of the baffles and then downwardly in the outlet chamber I42 from the lower end of which the gases are discharged through the outlet 93,

Although an air heater 4'! like: thatshown in 16" Fig. 1 and described above" is not embodied in the modification of Figs. 10 to 13, it is to beunderstood that such an air heater may be included in a manner generally like that illustrated in the first embodiment- In the modification of Figs. 10 to 1-3 the casing of motor 20 is provided with studs 2Ia' which pass upwardly through sleeves 22a formed integrally with the bottomplate I23;

and the motor is drawn tightly against the ends:

- I01, and the air then passes upwardly throughannular space- I!" between the casing 96:: and the outer element 89', annular space I05 between the two elements- 89, and annular space 106a betweenv the motor 20' and. the'inner element 8.9. The air which has been heated in these passages. passes into the space I43 at the upper part of casing Site from which it is discharged through a single duct socket 91a withinwhich may be located thermal devices I33 and I35 similar to those, previously described in connection with the first embodiment,

As shown in Fig. 10, the lower ends of angle: members I44 are secured to the outer element 89 and the upper ends thereof are removably' se cured at I45- to bosses I46 formed on the bottomplate I0, thereby providing a rigid and; unitary heater structure. The outer casing 96a is removably secured at its upper end at IN t the outer edge portions of the plates I0 and II. Suitable flanged legs I48- may be secured to the end cover III) to facilitate the mounting ofv the heater in an airplaneor other place'of use:

When. the heater of the invention is installed in an airplane I49, as diagrammatically shown in- Figs. 14 and 15, combustion air may be drawn into the impeller chamber I4 from the immediate surroundings of the heater within the airplane. A suitable connection I50 may be provided from the outlet 93 to the exterior of the ship for discharging the spent products of combustion overboard. It is desirable to operate the heater withv the heating spaces 92 at a pressure below that of atmospheric, and this may be accomplished by providing the connection I150 from the outlet. 93 to the exterior of the ship in-such a manner that, a suction. effect will be produced. at the extreme outer end I5I during flight of the airplane which. is reflected back to the annular. heating spacesfif. A suitable adjustable valve l52'may be provided in connection I50 and. a pressure gauge I53 may be connected between the valve and the outlet 93.

When the heater illustrated in- Figs. 10 to 13 inclusive and described above isoperated in an airplane, the valve I52 may be adjusted so that the pressure in the heating spaces is reduced below the pressure of the atmosphere within the interior of the airplane. byan amount, for exampla whichis equivalent to as much as five inches of water column; By providing a restricted outlet at 84a for the combustion chamber 83a and a restriction to the flow of the high temperature gases at 84g before. entering the heating spaces 92, the full effect of the negative pressure produced in the heating spaces isnot reflected back into the combustion chamber a, Thus; eventhough a den nite negative pressure is produced in the heating spaces 92, combustion can be-accomplished in the chamber 80:: at a higher pressure than that prevailing in the heating spaces so that combustion conditions will not be adversely affected by the negative pressure prevailing in the heating spaces.

Since combustion is accomplished at the highest possible temperature in chamber 80a by restricting the combustion chamber outlet, as explained above, and under such conditions the products of combustion are heated to the highest possible temperature, it will be immediately evident that it is of considerable advantage to be able to maintain the heating spaces at a definite negative pressure with respect to the atmospheric pressure of the environment in which the heater is being operated, and yet prevent the full negative pressure in the heating spaces being reflected or transmitted back to the combustion chamber 80a.

Further, the provision of a restricted outlet for the combustion chamber 80a promotes stable combustion over a wide range of operating conditions encountered in airplane heating. When movement of an airplane in flight is relied upon to develop the negative pressure in the heating spaces 92, as just explained, the negative pressure produced at the extreme end l! of the connection I50 may vary over a wide range which is dependent upon a number of factors including the speed and altitude of the airplane as well as the turns or banks of the ship in flight. The negative pressure developed during flight of the airplane due to these factors may vary over a pressure range equivalent to 15 or more inches of water column.

In some cases the resistance in the connection I50 alone maybe sufficient to produce and develop the desired negative pressure in the heating spaces, and it may be desirable under certain conditions to provide a restriction like that of the valve I52 which is either adjustable or fixed when the resistance in the connection alone is not sufficient. Although the negative pressure in the heating spaces 92 may vary over a considerable range, and at certain times may tend to be higher than desired, this is not detrimental to reliable operation of the heater because of the independence of the manner in which combustion is accomplished in the combustion chamber 80a and the provision of the restricted outlet between this chamber and the heating spaces 92 into which the high temperature gases pass.

In the embodiment of Figs. 1 to 8 the outlets 8| for the combustion chamber 80 are not restricted to the same extent as the outlets Me in the modification of Figs. 10 to 13. When the combustion chamber outlets are not restricted sufficiently, the full eifect .of the negative pressure developed in the heating spaces 92 may be reflected backto the refractory lined combustion chamber. In such case it is desirable to provide a valve I52 or other suitable fixed restriction, such as a small orifice, for example, in the connection 1 50 so that the negative pressure developed in the heating spaces 92' will not exceed a predetermined maximum value. It is to be understood, however, that in the embodiment of Figs. 1 to 8 the refractory post 84 and hollow refractory block 82 maybe shaped to provide outlets BI which are sufficiently restricted like the restricted outlets 84a in the modification of Figs. 10 to 13, sothat the full effect of the negative pressure; developed in the heating. spaces 92 will not be reflected or transmitted back to the combustion chamber and the combustion accomplished in the combustion chamber will be more or less independent of the negative pressure prevailing in the heating spaces 92.

It has previously been stated that expansion of the air and fuelmixture passing through the small inlet openings 16 takes place in the channels or grooves 19-formed between the ridges or walls 18. This .is particularlyhelpful when the heater of the invention is employed in aircraft heating, because the proportion of air in the mixture increases with increase in altitude in order to maintain the desired weight ratio of air to fuel. Since larger volumes of air mix with a given amount of fuel with increase in altitude, the expansion of the mixture in the grooves 19 with consequent reductionv in velocity helps to overcome any tendency for the flames to blow off the discharge ends of the inlet openings 16. The fact that combustion .is accomplished in a refractory lined combustion chamber in which heat is radiated from the incandescent lining also contributes to maintain stable combustion conditions at all times, and hence insure the flames always being rooted to the discharge ends of the inlet openings.

The air heater 4! in the embodiment of Figs. 1 to 8 is particularly useful when it becomes necessary tostart operation of the heater at extremely low temperatures, such as minus 40 F. and lower, which sometimes occurs in aircraft heating. In such case the closing of the switch l20 in Fig. 9 completes the circuit for the air heater 4! because thermal device I34 will then be in its closed position. This effects heating of the combustion air being drawn into the impeller chamber l4 by the impeller [55, and helps to facilitate rapid ignition of the air and fuel mixture in the combustion chamber by the electrical ignitor 85. When the heater reaches a temperature of about 70 F., as previously explained, the thermal device I34 opens and disconnects the heater'4'l from the source of electrical energy.

The heater providedis extremely efilcient and capable of producing an exceptionally high heat output per pound of heater. In a heater which has been built and generally like that illustrated in Figs. '10 to 1-3, and from which the drawings were made to scale, the heat .output is about 2,000 B. t. u. per hour per pound .of heater. The heater just referred to is18 inches in diameter, 14 inches in over-all height and. weighs approximately 12 pounds. The motor for driving the air fan l-Ma and. .impeller .l.5,and corresponding to the motor 20, isachighlspeed series motor rated at /8 P. The motor speed at sea level is about 10,000 R. P. andzat an altitude of 30,000 feet is'about 15,000'R. PLM.

The fact that a series motor operates at increasingly higher speeds with increase in altitude, due to decrease in air density, is particularly helpful in maintaining thev desired Weight ratio of combustion air to fuel under all of the varying operating conditions encountered in airplane heating. By properly adjusting the altitude compensator, and taking'into consideration the rate at which the speed-of themotor 2-0 increases with increase in altitude, it is possible to maintain the desired weight ratio of air to fuel under all operating conditions from sea level to altitudes of 30,000 feet and higher.

The heater referred to above and weighing about 12 pounds, is capable of producing 25,000 E. t. u. per hour at sea level and about 19,000 B. t. u. per hour at an altitude of 30,000 feet. The heater is capable of producing an average temperature rise of about 300 F. and a maximum temperature rise of 400 F. when air to be heated is circulated through the heater, and discharges heated air at the rate of about 150 cubic feet per minute. When gasoline is employed as the liquid fuel, the fuel consumption is about 1 /2 pounds of gasoline per hour (A gallon) to produce the heat output stated above, and with this rate of fuel consumption the heater efiiciency is about 85 per cent.

During operation of the heater the mixture of relatively cool combustion air and atomized fuel passing from the annular chamber [2 into the manifold 13 exercises a cooling effect and keeps down the temperature of the manifold. In the heater'referred to above the cross sectional area of the small openings 76 in the apertured inlet wall are about 0.3 square inch. The pressure of the mixture of combustion air and atomized fuel at the upper part of the manifold I3 is equivalent to about 1 inches of water column, and it has been observed that this pressure remains substantially constant under all operating conditions from sea level to an altitude of 30,000 feet and higher. The pressure drop of the air and fuel mixture through the small inlet openings 16 is equivalent to about inch of water column.

The combustion effected in the refractory lined combustion chamber is exceptionally clean, and, after many hours of heater operation, there has been a complete absence of carbon deposit in the combustion chamber. The fact that liquid fuel is introduced into the combustion chamber in an atomized condition is a distinct advantage when leaded gasoline is employed as the fuel, because the likelihood of lead vapors condensing in the small inlet openings 16 is avoided. In the heater actually built and operated under the most adverse conditions, the small inlet openings have remained free and open although operated at all times with leaded gasoline of high octane rating.

The heater of the invention is formed of a relatively few parts and is readily assembled and aligned. After securing the motor 20 to the bottom plate W by the studs 2! in the embodiment of Figs. 1 to 8, and positioning the impeller I at the upper end of the shaft 23 by set screw 24, the plates l0 and ll are then secured together. The annular shield I02 may then be secured to the underside of the plate H! by screws I03, as shown in Fig. 1. The altitude compensator including the bellows 42 and valve 3'! are mounted on a single part which is inserted into the openended casing 28, as shown in Fig. 7 and pre-' viously described. The casing 28 is secured to the top plate I I so that the hollowpost 53' is in alignment with the passage 58 in top plate H, and it is for this reason that the flange 29 of casing 28' is of irregular shape and similar to that of the boss or raised portion on top plate H to which the casing is secured, as previously described.

The annular elements 89 and metal shell 12 are formed as a single unitary structure, and the upper end of the shell 12 is secured to the flange at the bottom of the leg 65 which is formed integrally with the bottom plate (0, as best shown in Fig. 4. With this arrangement, the annular elements 89 are properly positioned and aligned concentrically about the motor which is also secured to the bottom plate Ill. The metal shell 12 serves as the housing for the burner parts and is easily accessible by simply removing the shell from the hollow leg 65. Before securing the shell 72 to the leg 65, the burner parts comprising the manifold 13 and the hollow refractory block containing the post 84 are simply slid into the shell 12 within which the parts snugly fit, as best shown in Fig. 6.

After securing the fan I01 to the shaft I08, the outer casing 86 can then be slipped over the elements 89 and rotated slightly so that the bayonet slots 99 at the top edge of the outer casing are locked by the pins 98 at the periphery of the plate 40. The assembly of the heater is then completed by securing ignitor and hollow tube 88 in the openings provided for these parts in the metal shell 72, as shown in Fig. 1.

In the heater of Figs. 10 to 13 the altitude compensator is of simpler construction than that in the embodiment of Figs. 1 to 8 and fewer parts are employed in that no combustion air heater 4'! or annular shield 102 about the motor 20 are included in the structure. The ignitor 85 in Fig. 10 is of a different type than that shown in Fig. 1 and described above and includes a ceramic core I55 having a helical groove about which is wound a hot wire heating element I55. The ceramic core is positioned close to the apertured wall 15 with the ridges 18 being cut away to form a recess to receive the ceramic core, as shown in Fig. 11.

In the embodiment of Figs. 10 to 13 the labyrinth packing 26a is formed by the hub of the impeller 45 and the hub of a rotatable element i511, which is secured to the shaft 23 in any suitable manner before the motor 20 and bottom plate I0 are secured together. The element [5a is formed with a plurality of blades 15b so that, in the event an occasional drop of fuel should pass downwardly from the packing 26a, it will not enter the upper end of the motor 20 but will be thrown radially outward by the blades I51) between the hollow sleeves 22a into the space I43. Such fuel vaporizes and mixes with the heated air in space 143 and passes out of the heater through the duct socket 91a.

The assembly of the heater of Figs. 10 to 13 is generally similar to that of the first embodiment just described. In the assembly of the modification of Figs. 10 to 13, the refractory block 84a is slipped into the metal shell 7211 at the uncovered part normally occupied by the manifold 12 and then moved sidewise into the covered part of the shell 12a having the side walls 12b. The hollow refractory block 82 and manifold 13 are then positioned within the shell 12a, so that the apertured wall 75 fits snugly within one end of the hollow block 82, as shown most clearly in Fig. 11.

It will now be understood that in the first embodiment and in the modification of Figs. 10 to 13 the parts of the burner assembly are insertable in and removable from the metallic shell or housing 72 and 12a when the heating unit is disconnected from the bottom plate ID of the impeller housing, thereby facilitating inspection and repair of the heater when this becomes necessary. From the above it will now be understood that the heater parts are readily assembled to form a single compact unit, and that the heater parts are accurately aligned and rigidly secured to the plates 10 and H forming the impeller housmg.

In view of the foregoing, it will now be seen that a compact and light weight heater has been provided in which the heat output per pound of 21 heater is exceptionally high-and in which dependable and reliable operation is assured under differ ent operating conditions, particularly those existing when the heater is employed for heating an airplane.

In the installation of the heater in the airplane MB, as diagrammatically illustrated in Fig. 14, the connection I50 extends upwardly from the heater. Condensationof water vapor accompanying the exhausted gases may take place in the exhaust connection, and in practice it is desirable to lead the connection for the exhaust gases downwardly from the heater, so that any condensate formed therein will drain by gravity and be discharged overboard;

Although several embodiments. of the invention have been shown and; described, it will be apparent to'those skilled in, the art that changes can be readily made and that certain features can be used independentlyof others without departing from the spirit and scope of the invention. In the heater of the invention, for example, the apertured inlet Wall of the refractorylined com.- bustion chamber may be formed or brass or othersuitable material as well as refractory material. Further, the negative pressure in the heating spaces 92 may be produced by a blower provided in the connection through which, the gases are exhausted from the heater at the outlet 93;. Such a blower may be driven by a separate electric motor or it may be like the blower which delivers combustion air and fuel to the heater and arranged to be driven by the same electric motor driving the air circulating fan'an'd impeller l5. We therefore aim in the appended claims tocover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

1. A heater complisingstructure including a blower adapted to supplya, combustible fuel mixture under pressure, said blower comprising a pair of removably secured opposing wall members providing an inner chamber having an inlet and an outer annular diffusing chamber immediately adjacent to and communicating with the inner chamber substantially about the entire periphery thereof, a rotatable impeller in the inner chamber, the outer annular chamber having an outlet for discharging combustible fuel mixture therefrom under pressure, a burner unit, means; for removably securing saidburner unit to one of said wall members to receive the combustible fuel mixture adapted. to be discharged from the outlet of the outer annular chamber, a hollow heat dissipating element connected to receive heated gases from the burner unit and through, which such gases are adapted; to. pass, means including a fan for circulating airto be heated in heat exchange relation with the hollow; element,,and means including a motor removably secured. to said one of said wall members for driving the impeller and the fan.

2. A heater comprising structure including a blower adapted to supply a combustible iuel. mixture under pressure, said blower comprising a pair of removably secured opposing wall members providing an inner chamber having an inlet and an outer annular difiusing chamber immediately adjacent to and communicating with the inner chamber substantially about the entire periphery thereof, a rotatable impeller in the inner chamber, the outer annular chamber having an outlet for discharging combustible fuel mixture therefrom under pressure, means providing a housing having an opening, a burner unit insertable into and removableirom the housing through the opening therein, said burner unit including.

a shell and refractory means, said shell having an apertu-red wall and an inlet adapted tu bo- 5- positioned adjacent the open end of the housing and said refractory means providing a refractory lined combustion chamber adjacent the apera turedwall, means for removablysecuringsaidhousingat the opening therein to one of said wall members to close the opening and connect theinlet of the shell for the latter to. receive combustible fuel mixture discharged fromxthe outlet of'the outer annular chamber; a. hollowheat dissipating element communicating with the-combustion space and through which heated gases from the latter are adapted to pass, means. including a fan for circulating air to be heated in heat-exchange relation with the hollow element, and means including amotor removably secured; to one of said wall members for driving the inpel'lerand the fan.

3. A heater comprising a frame having an out let opening, a blower mounted in saidframe to supply a combustible fuel mixture under pressurethrough said outlet opening, means providing a substantially straight elongated housinghaving an openingat one end thereof, a burner: unit insertable into and removable from the-housing through the opening therein, said burner unit comprising means providing a substantially straight elongated inlet space having an apcr-. tured side wall and an inlet adapted to be-positionede adjacent to the open end of the housing and refractory means providing an elongated refractory lined combustion chamber alongside the inletspace adjacent to said apertured wall, said apertured wall and elongated combustion chamberbei-ng substantially coextensive with thelength of the inlet space, a hollow heat dissi-v patingelement extending-from a sidewall of the housing and communicating with the combustion chamber and through which; heated gases firom the latter are adapted to pass, said hollow: ale-- ment; being substantially coextensive with the length-of the combustion space, and means for removably securingthe housing at theopen end thereof to said frame to close the outletv open ing in said frame and cause the: combustible fuel mixture to be delivered under pressure .totthe inlet space through the inlet of said burner unit.

4. A heater comprising a blower including :a. casing providingan inner chamber having inlet andan outerannular diffusing chamber immediately adjacent to and communicating 55 with the inner chamber substantiallyabout', the entire periphery thereof, a rotatable impellersln the inner chamber for drawing air therein through the inlet, means providing a passage through which liquid fuel isadapted to pass 60 from a source of supply into the inner'chamber for atomization therein by the rotatable inn. peller, saidouter chamber having an outlet. for. the mixture ofair and atomized fuel, a humerunit including structure providing an elongated c inlet space having one end thereof commnnia ating with the outlet of said outer annular chamber and a combustion space and an aper turecl wall therebetween, said elongated inlet space in its longest dimension being substantially 70 normal to the plane of rotation of the impeller and extending from said casing at the outlet of the outer chamber whereby said burner unit and casing may be readily separated, a hollow element communicating with the combustion 75 space and through which heated gases from the 23 latter are adapted to pass, means including afan for circulating air to be heated in heat exchange relation with the hollow element, and means for driving the impeller and the fan.

5. A heater comprising a blower including a casing providing an inner chamber having an inlet and an outer annular diffusing chamber immediately adjacent to and communicating with the inner chamber substantially about the entire periphery thereof, a rotatable impeller in the inner chamber for drawing air therein through the inlet, means providing a passage through which liquid fuel is adapted to pass from a source of supply into the inner chamber for atomization therein by the rotatable impeller, said outer chamber having an outlet for the mixture of air and atomized fuel, a burner unit including structure providing an elongated inlet space having one end thereof communicating with the outlet of said outer annular chamber and a combustion space and an apertured wall therebetween, means to attach said burner to said casing with said elongated inlet space in its longest dimension being substantially normal to the plane of rotation of th impeller and extending from said casing at the outlet of the outer chamber, means including a member in the outer annular chamber at the down stream side of the outlet thereof to facilitate the change in direction of the air and fuel mixture from the outer annular chamber into the elongated inlet space substantially normal thereto, a hollow element communicating with the combustion space and through which heated gases from the latter are adapted to pass, means including a fan for circulating air to be heated in heat exchange relation with the hollow element, and means for driving the impeller and the fan.

6. A heater comprising a blower including a casing providing an inner chamber having an inlet and an outer annular diffusing chamber immediately adjacent to and communicating with the inner chamber substantially about the entire periphery thereof, a rotatable impeller in the inner chamber for drawing air therein through the inlet, means providing a passage through which liquid fuel is adapted to pass from a source of supply into the inner chamber for atomization therein by the rotatable impeller, said outer annular chamber having an outlet for the mixture of air and atomized fuel, an annular-shaped heating unit adjacent to and at one side of said casing, said heating unit including a hollow element and burner structure providing an elongated inlet space having one end thereof communicating with the outlet of said outer annular chamber and a combustion space and an apertured Wall therebetween, means to attach said heating unit to said casing with said elongated inlet space in its longest dimension being substantially normal to the plane of rotation of the impeller and extending from said casing at the outlet of the outer chamber, said hollow element communicating with the combustion space and through which heated gases from the latter are adapted to pass, means including a fan for circulating air to be heated 24 in heat exchange relation with said heating unit,'and a motor having shaft means to which the fan and impeller are secured.

'7. A heater comprising a blower including a casing providing an inner chamber having an inlet and an outer annular diffusing chamber immediately adjacent to and communicating with the inner chamber substantially about the entire periphery thereof, a rotatable impeller in the inner chamber for drawing air therein through the inlet, means providing a passage through which liquid fuel is adapted to pass from a source of supply into the inner chamber for atomization therein by the rotatable impeller, the outer chamber having an outlet for the mixture of air and atomized fuel, a burner unit including structure providing an elongated inlet space having one end thereof communicating with the outlet of said outer annular chamber and an elongated combustion space alongside of the inlet space and an apertured wall therebetween, means to attach said burner unit to said casing with said elongated inlet space in its longest dimension being substantially normal to the plane of rotation of the impeller and extending from said casing at the outlet of the outer chamber, said apertured wall and elongated combustion space being substantially coextensive with the length of said inlet space, and a hollow element communicating with the combustion space and through which heated gases from the latter are adapted to pass, said hollow element being substantially coextensive with the length of the combustion space, means including a fan for circulating air to be heated in heat exchange relation with the hollow element, and means for driving the impeller and the fan.

FREDERIC o. .I-IESS. LAWRENCE F. MILLER. KARL L. DIETRICH, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,719,466 Evans et al. July 2, 1929 1,753,360 Brown Apr. 8, 1930 1,755,727 Cramer Apr, 22, 1930 1,981,976 Wem Nov. 27, 1934 2,011,606 Barthel et al. Aug. 20, 1935 2,157,653 Westwick May 9, 1939 2,165,269 Karsel July 11, 1939 2,175,812 Meyerhoefer Oct. 10, 1939 2,270,824 Meyerhoefer Jan. 20, 1942 2,314,089 Hess et al. Mar. 16, 1943 2,324,010 Meyerhoefer et al. July 13, 1943 2,324,540 Ryden et al. July 20, 1943 2,336,609 Herbster Dec. 14, 1943 2,364,458 McCollum Dec. 5, 1944 2,388,970 Hess et al. Nov. 13, 1945 2,410,548 McCollum Nov. 5, 1946 FOREIGN PATENTS Number Country Date 103,295 Australia Feb. 17, 1938 

